1. Field
The inventions disclosed and taught herein relate generally to drill bits for use in drilling operations in subterranean formations. More particularly, the disclosure relates to hybrid drill bits, and apparatus and methods for increasing the strength and extending the wear life of the support surfaces and bearing elements in such drill bits.
2. Description of the Related Art
Drill bits are frequently used in the oil and gas exploration and the recovery industry to drill well bores (also referred to as “boreholes”) in subterranean earth formations. There are two common classifications of drill bits used in drilling well bores that are known in the art as “fixed blade” drill bits and “roller cone” drill bits. Fixed blade drill bits include polycrystalline diamond compact (PDC) and other drag-type drill bits. These drill bits typically include a bit body having an externally threaded connection at one end for connection to a drill string, and a plurality of cutting blades extending from the opposite end of the bit body. The cutting blades form the cutting surface of the drill bit. Often, a plurality of cutting elements, such as PDC cutters or other materials, which are hard and strong enough to deform and/or cut through earth formations, are attached to or inserted into the blades of the bit, extending from the bit and forming the cutting profile of the bit. This plurality of cutting elements is used to cut through the subterranean formation during drilling operations when the drill bit is rotated by a motor or other rotational input device.
The other type of earth boring drill bit, referred to as a roller cone bit, developed out of the fishtail bit in the early 1900's as a durable tool for drilling hard and abrasive formations. The roller cone type of drill bit typically includes a bit body with an externally threaded connection at one end, and a plurality of roller cones (typically three) attached at an offset angle to the other end of the drill bit. These roller cones are able to rotate about bearings, and rotate individually with respect to the bit body.
More recently, a new type of earth boring drill bit that has made a presence in the drilling arena is the so-called “hybrid” drill bit, which combines both fixed cutting blades and rolling cones on its working face. The hybrid drill bit is designed to overcome some of the limiting phenomena of roller cone and fixed-cutter PDC bits alone, such as balling, reducing drilling efficiency, tracking, and wear problems. While PDC bits have replaced roller cone bits in all but some applications for which the roller cone bits are uniquely suited, such as hard, abrasive, and interbedded formations, complex directional drilling applications, and applications involving high torque requirements, it is in these applications where the hybrid bit can substantially enhance the performance of a roller cone bit with a lower level of harmful dynamics compared to a conventional PDC bit. Some of these hybrid drill bits have been described, for instance, in U.S. Patent Publication Nos. 2008/0264695 and 2009/0126998, and in IADC/SPE Paper No. 128741 (“Hybrid Bits Offer Distinct Advantages in Selected Roller Cone and PDC Bit Applications,” R. Pessier and M. Damschen, 2010).
Regardless of the type of drill bit used, earth boring drilling operations occur under harsh and brutal conditions, often in the presence of extreme pressures, temperatures, and sometimes even hostile chemical environments. Further, the bits are subjected to extremely demanding mechanical stress during operation, such as high-impact forces, high loads on the drill bit associated with faster rotation speeds and increased penetration rates, and the like. Of the numerous components of the drill bits that suffer under these conditions, particularly in the case of bits having one or more roller cone type bits, the bearings in the drill bit can be particularly vulnerable, with their failure resulting in bit malfunction and premature bit removal from the well bore, which in turn results in lost time and drilling progress. Consequently, much effort has been devoted over the years to improving the wear, impact resistance, and load capacity of bearings and bearing assemblies for use in earth-boring drill bits.
For example, U.S. Pat. No. 4,260,203 describes a rotary rock bit having bearing surfaces utilized therein which have extremely long wear resistant properties. The rock bit comprises a plurality of legs extending downwardly from a main bit body. A cone cutter is rotatively mounted on a journal formed on each leg. One or more of the inter-engaging bearing surfaces between the cone and the journal includes a layer of diamond material mounted on a substrate of carbide. In one embodiment, the bearing material forms the thrust button adjacent the spindle located at the end of the journal. In another embodiment, the bearing material is located on the inter-engaging axial faces of the journal and cone. In still another embodiment, the bearing material is a segmented cylindrical bearing located in a circumferential groove formed in the journal.
In U.S. Pat. No. 4,729,440 to Hall, an earth boring apparatus is disclosed, the apparatus having bearing members comprised of transition layer polycrystalline diamond. The transition layer polycrystalline diamond bearings include a polycrystalline diamond layer interfaced with a composite transition layer comprising a mixture of diamond crystals and precemented carbide pieces subjected to high temperature/high pressure conditions so as to form polycrystalline diamond material bonded to the precemented carbide pieces. The polycrystalline diamond layer acts as the bearing surface. The transition layer bearings are preferably supported by a cemented tungsten carbide substrate interfaced with the transition layer.
In U.S. Pat. No. 4,802,539, also to Hall, a roller cone rock bit is disclosed with an “improved bearing system.” The improvement reportedly comprises a main journal bearing which is substantially frustoconically (or cone) shaped and a main roller cone bearing which is reverse-shaped so as to be able to mate with the journal bearing. The journal and roller cone bearings comprise polycrystalline diamond. The invention also describes a member for retaining the roller cone on the journal, as appropriate.
Despite these proposed approaches, they often have suffered from material deficiencies, machining difficulties, or the like, leaving the need for improved bearing systems for use with roller cone drill bits. The inventions disclosed and taught herein are directed to drill bits, including, but not limited to, hybrid-type drill bits, having an improved bearing system for use with the roller cones on the drill bit.